Low-cost austenitic complex concentrated alloy with deformation-induced plasticity and nanoprecipitate as a strategy to enhance energy absorption at cryogenic temperature: Computational modeling and experimental validation

The development of multicomponent alloys for cryogenic applications requires reliable prediction of phase stability to ensure adequate toughness at low temperatures. This is critical to address the embrittlement phenomenon observed in conventional alloys under cryogenic conditions, as in the case of austenitic stainless steels such as 304 L and 316 L, which suffer toughness degradation due to the formation of martensitic (α′) phase. In this context, the present work focused on the development of a complex concentrated alloy (CCA) based on the FeCrNiCuTiVC system, fabricated by induction melting under an argon-controlled atmosphere, using primarily recycled stainless steel and ferroalloys as raw materials. The alloy design was carried out through an integrated approach combining machine learning techniques (Random Forest and XGBoost) trained on a robust database of 2591 records, together with thermodynamic predictions via CALPHAD using the TCHEA6 database. The resulting alloy exhibited an austenitic matrix with fine-scale precipitate-like features and the formation of σ phase. Tensile tests revealed an elongation of ∼82 % and a strength–ductility product (PSE) of 40.1 GPa·%, evidencing high damage tolerance. Nanoindentation and microhardness results indicated that the σ-phase precipitates do not exert a significant macroscopic effect in this alloy, which accounts for its remarkable deformability. Furthermore, nanoindentation tests revealed pop-in events characteristic of twinning, suggesting the activation of a twinning-induced plasticity (TWIP) mechanism. This was evidenced by SPM analyses of the nanoindentation imprint and by FE-SEM observations in the post-fracture sample. Similarly, fine-grained regions were identified in the area adjacent to the fracture, originating from subgrain formation caused by the severe dislocation interactions within the material. This explains the high ductility observed and validates the pronounced strain-hardening behavior of the alloy. Finally, Charpy impact tests demonstrated energy absorption of 205 J/cm² at room temperature and 226 J/cm² at 77 K, indicating not only excellent toughness at cryogenic temperatures but also the absence of a ductile-to-brittle transition, even in the presence of intermetallic phases. This behavior is attributed to the synergy between the TWIP mechanism and nanoprecipitates, both of which enhance the mechanical response and suppress premature embrittlement potentially induced by the σ phase, given its reduced fraction in the microstructure.